Scanning near-field photon emission microscopy

Abstract

The resolution of fault isolation techniques, like far-field photon emission microscopy (FFPEM), is grossly inadequate for advanced semiconductor technology nodes beyond 65 nm. The fundamental limit on spatial resolution of FFPEM is approximately half the wavelength of the detected photons. The practical limit is slightly less than 1 ¿m. FFPEM with such a resolution is not only incapable of identifying the faulty transistor but it also cannot identify the faulty functional block in the integrated circuit (IC). Near-field optical detection using scanning near-field photon emission microscopy (SNPEM) promises resolution capabilities below 100 nm. However, existing implementations of SNPEM have serious limitations in terms of photon emission detection efficiency, repeatability and applicability to different samples. The quality of near-field detection is mainly determined by the properties of a near-field probe. Different near-field probe designs are available but they have certain disadvantages that can limit their application in SNPEM. To overcome these, eight requirements are formulated in this thesis to rank the existing probes. Using this ranking the uncoated dielectric probes are chosen and applied for SNPEM detection from a variety of test structures. A detection efficiency level of 10 microA in terms of variation of the biasing current through the transistor is demonstrated. However, such detection efficiency is achieved through the compromise in resolution to approximately 200 nm.

In order to improve the SNPEM imaging quality, a novel concept of a scattering dielectric probe with embedded metallic scatterers is proposed. In this concept, a metallic nano-particle is embedded into the nanometric tip of the tapered dielectric waveguide. In order to fabricate such a probe, an implantation of gallium (Ga) atoms using a focused ion beam is implemented. A unique fabrication method allows us to perform the implantation simultaneously with the formation of the nanometric tip, making this method simple and repeatable. The performance of such a Ga-based scattering dielectric probe (Ga-SDP) is evaluated. A theoretical prediction of the scattering efficiency for a Ga nanoparticle shows that an enhancement of approximately 20 times can be expected in comparison with a similar sized nanoparticle made of silica. The experimental comparison of Ga-SDP and silica tips shows that the enhancement can reach a value of 37. It is suggested that such a high value originates from the modified dielectric function of the Ga-silica composite in comparison with pure Ga used for the theoretical evaluation. The application of Ga-SDP for SNPEM shows that a resolution capability in the order of 50 nm is achievable. The lowest detected variation in the biasing current is below 1 microA. This makes SNPEM with Ga-SDP suitable for the detection of the leakage currents in current and future technologies. Wavelength dependent SNPEM measurements show the possibility for distinguishing different photon emission phenomena within the single emission spot. It is also shown that the position of the emission source below the surface, as well as the probe-sample distance regulation, have a strong influence on the recorded images. Reduction of these two parameters leads to substantial benefits in terms of both spatial resolution and detection efficiency.